1. Field of the Invention
This invention relates to electronic systems for displaying time varying electrical signals and computing integrals of operator controlled segments of the signals and more particularly to such a system wherein the operator may specify integration boundaries after observing a pertinent section of the display.
2. Description of the Prior Art
In certain analytic systems it is desirable to provide an operator with a display of a time varying quantity as well as with information relating to the nature of certain segments of the curve thus generated, such as the values of segment integral. For example, it is common to analyze the protein constituents of a blood sample by electrophoresis. This involves placing the sample on a media and subjecting it to an electric field which will cause the protein fractions to migrate at rates dependent upon their molecular weights. The resultant "separation" may be analyzed by optically scanning it from end to end to generate a time varying electrical signal. When this signal is recorded on a chart it will provide a graphic representation of the densities along the sample and a trained operator can identify various segments of the curve with particular protein fractions of the blood. My U.S. Pat. No. 3,784,789 disclosed a system operative to generate the visual display of the time varying signal resulting from optically scanning the separation, and to compute the values of the integrals of various segments of the curve representative of particular protein fractions. In that system the boundaries between the fractions were first automatically generated by circuits which received the time varying signal and detected reversals in the sign of the differential of the displayed value. As the instantaneous magnitude of the signal was recorded on a moving chart it was also digitized and the values entered into a shift register along with the detected fraction boundaries. A control system generated clocking signals which powered the chart drive motor and the advance of the digital signals in the shift register in timed relationship to one another. A short time after a particular point in the signal was recorded on the chart paper, sufficient to allow an operator to observe the nature of the curve, the chart paper passed under a cursor and the operator could modify an automatically generated boundary decision through use of manual controls which allowed him to either delete a previously determined boundary or add a new boundary. These editing signals, along with the output of the shift register, were then provided to the computer which generated the integral values of the edited curve segments.
The system for driving the chart in timed relation to the advance of the digital signals in the shift memory was a relatively expensive part of the system and imposed certain limitations on the operation of the system. That synchronization was accomplished by clocking the memory with a power line derived signal and by employing a line synchronous chart drive motor. Alternatively, the chart drive motor could be of a stepping type controlled by a clock common to the motor and the memory.
Motors which can provide such precise chart paper control are generally quite expensive and stepping motors require a substantial amount of controlling electronics. It was also difficult to retrofit this manual editing feature to existing instruments equipped only with the automatic detection feature because of the need for changing the drive motor. Additionally, because of the requirement for constant speed for the drive motor, the operator was unable to modify the scale factor so that interesting sections of the curve could be observed in greater detail.
The present invention is directed toward a recording and computing system of this broad type employing a novel system for controlling the chart's speed and the advance of the stored signals in the memory relative to one another which is lower in cost and more flexible in operation than the previous system.